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Energy efficiency in buildings
When we talk about energy efficiency in buildings We usually refer to the set of procedures that lead to the I build consume less energyBut the crux of the matter is determining how far it is possible or reasonable to go.
State regulations inspired by the Energy Efficiency Directive usually take as a reference what is called “optimal cost”, which is that the investment costs are acceptable in relation to the economic benefits that the energy entails. lower energy consumption (optimization).
Note: You can consult the application of the «optimal cost» methodology in EU countries from HERE in English.
Although the economic viability, is it is not the only criterion possible and could try to reduce the energy consumption of the building until it is practically nil or that the environmental impact resulting from the construction and operation of the building is minimal (minimization).
It is evident that according to the different criteria adopted as a reference, the levels of ambition in obtaining energy efficiency will also be different.
In this article we will try to evaluate for a given building, what is the level of ambition provided by these different criteria and we will show that the most commonly used, which is energy optimization, leads precisely to being the least ambitious and we would do well in do not consider it as the preferred criterion.
Methodology
- We will use an example building and by modifying only the "insulation" parameter, the final energy consumption for Heating, Cooling and their auxiliaries (pumps and fans) will be evaluated.
- Consumption derived from lighting, equipment, sanitary hot water has been excluded from this study since these are independent of the level of insulation and it is precisely the latter that we wish to highlight, since on certain occasions some have claimed that a “Excess insulation” might not be recommended from an energy efficiency point of view.
- Once obtained for each isolation hypothesis, we will translate primary energy consumption into economic (cost) or environmental impact (GWP greenhouse effect).
- To make the results more easily usable for other similar building sizes, the results will be normalized according to the conditioned surface of the building.
- Finally, the results will be analyzed in the form of a point cloud graph where the trend of each variable is intuited when the amount of insulation available in the building increases.
Case study
It is considered for this case, a multi-family building between houses composed of ground floor + 4 floors with a total of 16 houses with a conditioned area of 1282 m2 (only the houses are considered conditioned)
The following image shows the building considered:
BUILDING CHARACTERISTICS:
- The orientation of the building is North-South.
- The construction is traditional with insulation materials in facades by means of cladding and flat roof with inverted roof.
- The insulators used are Glass Wool in the cladding and XPS in the inverted roof.
- For the insulation levels, 12 insulation levels for the facade and roof have been considered and the calculation has been made with all possible combinations with values ranging between 0 cm and 22 cm, which represents carrying out 144 cases.
- Double-glazed windows are available in the building in all cases.
- The occupational profile and ventilation management are those that are considered representative of the use for housing.
- The heating oil is natural gas while the one used in cooling and auxiliary is electricity.
- For the study, the tracings have been repeated for two sites (Barcelona and Madrid) to take into account the possible influence of the weather.
Software used
- Geometry has been used for modeling Sketchup.
- OpenStudio has been used to build the energy model
- The calculations have been made directly on the Energy Plus tool.
- Parametric calculations and extraction of results have been carried out with the help of JEplus.
- The analysis of results has been carried out using Excel.
Calculations
1.- Energy consumption
The first step consists of evaluating the amount of final energy consumed by the heating and cooling systems, including the associated consumptions of the fluid circulators.
In both cases, it can be seen that within the insulation levels considered in the study (between 0 and 22 cm) consumption is decreasing as the availability of insulation increases, and, therefore, it will always be positive to increase the insulation if desired. minimize energy consumption.
2.- Total cost
It is called “Total cost” to the sum of the costs derived from the investment in insulation and the operating costs of the building.
- For the investment cost in insulation, only the derivative of insulation has been considered, which is representative of the case of new construction.
- For the investment cost, only the energy term and its derived taxes based on the fuel have been considered and with a horizon of 50 years as the probable life of the building.
The results are reproduced below:
It is evident that, in this case, there is a value that provides a minimum total cost and that lower or higher insulation levels lead to an increase in cost.
It is also appreciated that the higher levels of insulation represent negligible total cost increases. While lower insulation levels, they provide considerable cost increases.
What is commonly referred to as the "optimal level" of insulation, is actually the "minimum level" below which we should never be in order not to include significant cost overruns.
3.- Environmental impact (Greenhouse Effect)
To evaluate the environmental impact due to the incorporation of the insulation, the Environmental Declarations of the Products (DAP / EPD) introduced in the building have been taken and the greenhouse effect (GWP) of each case has been considered throughout the life cycle.
Let's remember that we have an extensive article on how to calculate the environmental impact of a building and what programs, also written by Josep Sole.
In a similar way to how final energy consumption has been translated into operating cost, the greenhouse effect potential has been evaluated based on the type of fuel used. The results are summarized in the following graphs.
As with energy consumption, in this case, the total environmental impact throughout the entire life cycle is reduced by increasing the level of insulation without finding, at least within the environment studied, a limit value that cause an increase in the environmental impact of the building.
Consequently, contrary to what some claim, the amount of insulation to be installed in the building should in no case be limited for environmental reasons.
Conclusions.
- Parametric studies make it possible to reveal the evolution of energy consumption, cost or environmental impact by increasing the level of insulation available in a building.
- Within the limits studied, only for the economic criteria, there is a minimum value that does not match the maximum isolation level.
- The “optimal cost” criterion is the least ambitious of the possible criteria, and therefore should not be used preferentially as is usual.
- The criterion for minimizing environmental impact coincides with the criterion for minimizing energy consumption and it should be used preferentially as an energy efficiency criterion.
- The The decarbonisation objectives of buildings fundamentally go through a maximization of thermal protection thereof.
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